Each of the reactions for producing ethylene oxide, or the production of phthalic anhydride or maleic anhydride, is highly exothermic, involving the controlled oxidation of organic substances. Thus, it is necessary that the heat generated by the reaction be removed as efficiently as possible so as to prevent a run-away reaction in which undesirable products are produced and in which expensive raw materials are wasted. Accordingly, it has been the practice to utilize catalytic tubes of extremely narrow diameter. Thus, for example, it is not unusual for a catalyst tube to have an I.D. of 1.25 inches and to be 60 feet long. The reactor, however, may contain as many as 2500 to 9000 tubes. In one instance, for example, the reactor had tubes which were only 22 feet tall, but each tube had an I.D. of 3/4 inches and the reactor contained 8600 tubes. Each of the tubes are connected at each end to a tube sheet, and the entire bundle of tubes and tube sheet is jacketed and filled with a heat transfer fluid or medium, as, for example, Dowtherm, mercury, or molten salt solutions. Due to the heat given off by the reaction, the space velocity is maintained at an extremely high rate so that there is considerable abrasion of the catalytic spheres within the small diameter tubes. Additionally, hot spots can occur within the reactor. When this occurs, the catalyst bridges over and the tube may be lost from service. This, of course, depends upon the severity of the spot. Additionally, in the case of ethylene oxide, for example, one patentee points out that the optimum temperature for the reaction is in the range 225.degree.-250.degree. C. If the temperature falls below 225.degree. C., the conversion rate is insufficient to be economically feasible. If the temperature goes above 250.degree. C., the ethylene oxide selectivity decreases significantly with the concommitant loss of the desired end product. It is obvious, of course, that if the reaction gets too far out of hand that the end product is carbon dioxide and the catalyst becomes fused throughout the length of the 20-60 feet of small-diameter tubes.